As treatment of a core in machining the core with a wire electric discharge machine, there has been known a technology for transferring, while machining the core, an electrode component to a machining groove formed behind a wire electrode by the machining, filling the machining groove with the electrode component, and fixing the core, which should originally be separated from work, in the work (see, for example, Patent Literature 1). The machining by this technology is hereinafter referred to as fixation. By applying the fixation, it is possible to prevent the core from dropping from work during the machining. The core fixed to the work by the fixation is detached from the work when a physical impact is applied to the work after the work is detached from a machining table of the wire electric discharge machine.